Calculation of fault current in MMC-HVDC based on numerical inverse Laplace transform

Abstract

The fault transient analysis of the modular multilevel converter based high voltage direct-current (MMC-HVDC) system is an important basis for the refined design of protection strategies and the selection of equipment parameters. To truly reflect the current traveling wave process on the overhead line after the fault,it is necessary to introduce a distribution parameter model of the transmission line in the analysis. Firstly,the MMC in the fault stage is represented equivalently. Then,the equivalent circuit of the pole-to-pole fault of the DC system is established in the complex frequency domain. The fault current is solved by the nodal analysis method,and the analysis results obtained in the complex frequency domain are converted into the time domain responses by the numerical inverse Laplace transform (NILT). Finally,the NILT-based calculation results are compared with the electromagnetic transient simulation results for verification. The results show that the proposed method has high accuracy and can effectively reflect the propagation characteristics of fault traveling waves,which is of positive significance for the protection design of MMC-HVDC systems.

Keywords

• numerical inversion of laplace transform (nilt)
• high voltage direct current (hvdc)
• modular multi-level converter (mmc)
• overhead transmission line
• fault current calculation
• traveling wave process